For Matrix fans - and it's no exaggeration to say there are millions of them - the countdown has started. In exactly four weeks, the five-year wait for Matrix Reloaded and Matrix Revolutions will be over. The sequels to the most influential action film of the last millennium will be the hottest tickets in town.

The Matrix franchise is a phenomenon. The tale of a computer hacker who discovers that the world has been taken over by evil robots and that our universe is, in fact, a giant virtual-reality construct (ergo, nothing is real), the original movie made a staggering £290 million worldwide, making it Warner Brothers' biggest release ever.

It was also the first DVD to sell more than a million copies, and has inspired everything from books on philosophy to fashion collections. You can even buy Matrix wallpaper - based on the mysterious computer code the hero (played by Keanu Reeves) discovers.

Yet, following an extraordinary series of events, it's a miracle the £190 million sequels were ever finished. For, while media hysteria might be turning 2003 into the year of The Matrix (complete with scene-stealing world premiere at Cannes next month), it was 2002 that was meant to be the big one.

There were the deaths of two lead actors, the break-up of Keanu Reeves's relationship following the birth of his stillborn child, and mounting costs that almost scuppered production until Reeves dug deep into his own pockets. It's no wonder fans are whispering about the Curse of The Matrix.

The first shock was the death in a plane crash of R&B star Aaliyah, 22, who had not completed filming her role as Zee, a mysterious Matrix "goodie". The cast was distraught, and production was put back months by the need to reshoot Aaliyah's scenes. Finding a replacement was no mean feat, but finally Marvin Gaye's daughter, Nona, got the part.

Cast members talk of the punishing 270-day shoot in Sydney as a kind of emotional endurance test. Shortly after Aaliyah's death came the events of 11 September. Then, barely a month later, they were hit by the loss of another cast member, the much-loved Gloria Foster, who played The Oracle. She died of diabetes. "We lost our youth and our wisdom," said Laurence Fishburne (who plays Morpheus).

The troubles didn't stop there. A number of the special-effects houses commissioned to produce individual shots went bust, and costs rocketed. The fight scenes in the sequels are said to put those of the original (which introduced the spectacular "bullet time", where the camera appears to spin 360 degrees around its subject) to shame. But they cost the studio dangerous sums of money. One 17-minute helicopter battle through skyscrapers cost £25 million.

With costs spiralling, the production was in danger of collapsing. Reeves agreed to sign away his "back-end points" (a percentage of the profits of the film), worth £24 million. It's worth remembering, though, that Reeves was paid a £9.5 million fee up front for each movie and pocketed a tasty back-end bonus of £22 million after the astonishing success of The Matrix.

During production, Keanu's personal troubles began. In 1999, his girlfriend, Jennifer Syme, gave birth to their daughter stillborn. The couple split up not long afterwards, but remained close. Later that year, Reeves crashed his motorbike and ended up in hospital with broken ribs and a ruptured spleen. When filming started, he was back in hospital after injuring his foot shooting action scenes.

Then, in April 2001, Jennifer Syme was killed in a car crash in LA. To make things worse, Reeves found out that his sister, Kim, who had been battling leukaemia for 10 years, had suffered a relapse. He abandoned the set and flew her to Hawaii to make her more comfortable.

Of course, all this bad luck has only served to whet the appetites of etiolated youths hunched over computers across the globe. Conspiracy theorists - and serious Matrix fans who are by nature distrustful of perceived "reality" - might even believe some higher force was trying to prevent the films being made.

So what is the appeal of this sci-fi shoot-em-up? Well, first it pulled off the rare feat of almost universal appeal. Computer nerds thought it was the best thing since Windows; action fans were gobsmacked by its set-pieces and mindblowing effects; and on top of all this, it's "deep". With nods towards Plato and deconstructionist philosophy, the movie gave arthouse intellectuals a chance for a spot of guilt-free slumming.

Shot back-to-back, or rather as "one big movie chopped in half", Matrix Reloaded and Matrix Revolutions have been shrouded in a self-imposed burqa of secrecy. All we know is that Reloaded begins where The Matrix left off. The machines make a terrifying discovery: they've learned the location of Zion, the last human city, hidden near the Earth's core, and the humans have only 72 hours until thousands of Sentinels - the squidlike probes from part one - tunnel down to obliterate it. Their only hope is to track down a mysterious figure known as the Keymaker, who is being guarded by a pair of switchblade-wielding villains known as the Twins, unnaturally white assassins who can vanish and reappear like ghosts.

In addition to the now-iconic returning cast - Reeves as Neo, Fishburne as Morpheus, Carrie-Anne Moss as Trinity and Hugo Weaving as Agent Smith - Reloaded introduces new characters: a Buddha-like figure named Seraph (Collin Chou), Niobe (Jada Pinkett Smith), a former lover of Morpheus, and Persephone (Monica Bellucci), a deadly temptress with her eyes on Neo.

With all the feverish expectation, it's impressive that the film-makers have managed to keep such a tight lid on proceedings. Even in this age of on-set espionage and spoilers, we know practically nothing about the coming films except tidbits that can be gleaned from teaser stills and trailers.

Indeed, the writer/directors, Larry Wachowski, 37, and Andy Wachowski, 35, are shadowy figures with a disdain for the limelight. What is known is that the brothers have made a conscious effort to create the first true multimedia broadside at our hearts, minds and wallets. With the simultaneous release of the first sequel, a computer game, a companion DVD and nine animated short films (The Animatrix) you'll be hard-pressed to avoid the phenomenon.